PHY 2048L
Lab 3

Newton's Second Law

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Updated: 1/21/2013
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This lab is a fully revised, computerized version of Lab 8 in the manual. You should read the theory section of Lab 8, but all of the procedures and data sheet are on a handout. We will, however, still use the post-lab questions because the objective of the lab is unchanged. The SIGNIFICANT changes in this lab are described on a handout, which gives all of the procedures you will follow. (A copy of an older version of that handout is linked below.) Since we used the same motion detector during Lab Zero, some of the setup should be familiar to you.

Guiding Question:

Important: Be sure you support your answer with quantitative results from your measurements. Remember that agreement between theory and experiment concerns "accuracy" and is evaluated by using the percent error determined in the experiment.

Preparing for the lab:

Read the theory for "Lab 8" (pages 85 to 86) in the lab manual and answer the questions on LON-CAPA. Although the procedure will be quite different, none of the questions are about the procedure details.

Note that the LAST of the pre-lab questions requires doing a simple linear least-squares fit with Logger Pro. Plan ahead.

Comments

Review the handout linked below so you will have an idea of how to use the Data Studio software to make this measurement instead of having to do the labor by hand as we did in Labs 1 and 2.

It works best if you start taking data with Data Studio before you release the glider, and stop it after the mass hits the floor and the glider bounces back from the end of the track. The information you need to do this is similar to the info given about using the Data Studio program in Lab 7.

Note that you will make 5 measurements in this lab with the Data Studio program, recording them on the data sheet provided with the lab handout, and then do a linear least squares fit to the acceleration data with Graphical Analysis. This last step and the final analysis follows the lab manual, but the analysis of the raw data to get velocity curves and accelerations is completely different from the method shown in the lab manual.

A balance is supplied so you can measure the masses used to accelerate the puck. Experience shows that these masses can vary a small amount from their nominal value, and you will get more consistent results if you always measure the ones you use for a given run.

You also need to remember the comments from the last lab about the order of data in your calculation tables often being in exactly the wrong order for entry into Graphical Analysis. You enter the independent variable (t) first, not the dependent variable, v, regardless of how they appear in the data or calculation tables.


Apparatus

The blower should be plugged into the wall outlet, while the computer and the analog-digital converter should be plugged into the power bar on the front side of the lab table.

air blower, balance, air track with glider, masses, motion detector

(Computer used to run Data Studio is on the right.) The small masses will be used to accelerate the glider by hanging them from a string (not shown) over a white pulley on the left end of the air track.

Details

Motion Detector:
The initial setup by the laboratory staff might have placed the motion detector on the analog-digital converter next to the computer for safe storage (click link for a photo), but you should find it ready to be used, attached to the end of the air track with a rubber band.

If it does not appear to be attached properly, contact the lab instructor. The motion detector is expensive and has a very fragile transmitter. Please be very careful to avoid damaging it.
motion detector
motion detector and glider with reflector The motion detector must be aligned with the conical reflector on the glider.

The motion detector has a minimum range of about 15 cm, so we will never make measurements with it as close as you see here. We will set it up so it starts about 1/3 of the way down the track.

The calibration distance is from the detector to the point of the conical reflector. IMPORTANT: Do not touch the thin film on the front of the detector. It is very fragile. Measurements can be made from the side or top, aligning the meter stick by eye.

Extra Masses:

A key part of this lab is keeping the total mass of the system (m + M) constant while varying the mass "m" that provides the force to accelerate the system. The trick to doing this is to send the unused small masses along as passengers on the glider.

glider carrying extra masses

Notice how they can be hooked into the center rail of the glider. You might be careful to balance them on both sides, but that is not critical to having this work correctly.

Using Data Studio to collect the data

The details on how to use the Data Studio software to collect the data and determine the acceleration from the graph of velocity -vs- time is on the lab handout, but some of it is similar to the information given about using the Data Studio program in Lab 7.

 
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